It’s the middle of winter. Scott Brown has his shirt off, and it can only mean one thing. He’s running for US Senate in New Hampshire.

That’s the way the political press read the picture of a bare-chested Brown taking part in the Granite State’s 15th annual Penguin Plunge. Whether Brown was showing off his body or just avoiding the embarrassment of wearing his team’s official T-shirt — “Buckley’s Frozen Seamen” — his shirtless-ness during a charity plunge to benefit the Special Olympics was seen as a signal of intent to run against Democrat Jeanne Shaheen.

The former senator from Massachusetts, who recently sold his Wrentham home and moved full-time to New Hampshire, has yet to announce his plans. But Democrats are nervous, and they should be.

Shaheen is vulnerable; a recent poll showed her tied with Brown at 44 percent. To ward him off, a pro-environmental group is launching a $220,000 ad buy, Politico reported. Senator Elizabeth Warren of Massachusetts is raising money for Shaheen and warning Brown that her colleague will be hard to beat.

A recent tweet of Brown-generated gibberish triggered snide recollections of Brown’s “Bqhatevwr” tweet from a year ago, and photos from his law school modeling days are being resurrected, to undercut his credibility.

Chortle away. If Brown gets into the race, it’s a big political story with potentially serious consequences for Democrats anxious to retain control of the US Senate. And for Brown, Obamacare will once again be at the heart of it. In 2010, when Brown won the seat long held by Ted Kennedy, he campaigned on a promise to vote against the Affordable Care Act. He never got that chance.

Four years later, Shaheen’s vote in favor of the health care law is a very fruitful line of attack in New Hampshire, where 53 percent oppose it, according to a recent survey.

A quote from Shaheen that people can keep “their doctor and hospital no matter what their insurer does” is fodder against her, an awkward echo of President Obama’s false declaration that if you like your health insurance plan you can keep it.

Shaheen clearly sees political trouble with Obamacare. Last fall, she crafted a letter signed by 10 senators asking the Obama administration to delay the open enrollment period. And in a recent radio interview, she wouldn’t say if she would vote again for the health care law.

Brown, who supported Romneycare in Massachusetts in 2005, is also vulnerable to attack on that front from conservatives. He can expect primary challengers if he gets into this race, but it’s unlikely that would scare him away if he really wants to run. He leads former New Hampshire Senator Robert C. Smith more than 2 to 1, according to one recent Granite State poll.

The problem for opponents from the left or right is Brown’s ability to generate headlines, simply by removing his clothes. As far as the national press is concerned, Brown’s still got it.

After his demoralizing loss to Warren in 2012, that must cheer him up. Being out of Massachusetts should also be liberating. From the moment he went to Washington, Brown was caught between liberals back home and conservatives in the Senate. Walking that line was a nightmare for a senator from the Bay State. It could be easier to find a comfortable center in New Hampshire.

The poll that showed Brown tied with Shaheen also showed him leading among independents. Shaheen was ahead with women (46 to 30 percent), and Brown was ahead with men (51 to 40 percent).

So the women’s vote will be key. That’s where tone matters and can play to Brown’s advantage, along with what he casts as pro-choice credentials.

But that’s also where he stands to run up against Warren, his nemesis. She already raised $139,000 for Shaheen, and is making it clear that helping Shaheen win reelection is a personal priority. In her showdown with Brown, some of Warren’s most powerful moments came when she raised doubts about his commitment to abortion rights and other women’s health issues.

With Warren by her side, Shaheen has a better chance of keeping women on her side. She will need them all — and then some — if Brown flexes his muscle, political and other.

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